1. Field of the Invention
The present invention relates to a semipermeable membrane for blood treatment which exhibits little change in performance upon drying and reduced elution of a hydrophilic polymer therefrom; a dialyzer for use in blood treatment using the same; and a processes for producing a dialyzer having incorporated therein a semipermeable membrane which exhibits little change in performance before and after drying and reduced elution of a hydrophilic polymer therefrom.
2. Description of the Related Art
As a material for a semipermeable membrane for blood treatment such as an artificial kidney, there have been used a number of materials. For example, a natural material cellulose and its derivatives, e.g., cellulose diacetate and cellulose triacetate, were originally used, and synthetic polymers were then developed, such as polysulfone, polymethyl methacrylate (PMMA) and polyacrylonitrile. Recently, modified cellulose membranes have also been used which is prepared by treating cellulose with polyethylene glycol (PEG) or the like to modify the compatibility to blood. In semipermeable membranes for blood treatment in patients suffering from chronic renal failure, attempts have been made to reduce the leakage of albumin to a minimum while positively removing low molecular proteins other than albumin. In addition to such improvement in the membranes, hemodiafiltration (HDF) procedures and push-and-pull procedures have been developed for increasing the dialysis efficiency and positive removal of undesirable low molecular proteins. Polysulfone, which has a high water permeability, is now widely used since it meets the above-mentioned requirements. In a polysulfone membrane, a hydrophilic polymer is generally blended to impart an affinity for blood to the membrane. However, the polysulfone membrane has such a defect that once it is dried the properties tend to be changed to a great extent. Hence, it is difficult to produce a dry type of polysulfone membrane dialyzer which is light-weight and easy to handle.